DEEP

CONDITION SHEWN  NORMAl . •• LIGHT _...--- form . The additional weights that constitute the difference between light and deep load (i.e. cargo, coal, stores and water) are generally placed low down, and thus the position of the centre of gravity is usually lower when loaded than when light, causing an increase of stability which frequently more than compensates for the loss of stability indicated by the cross curves . The stability curves for the same vessel are reproduced in fig . 10 . It is customary in warships to draw separate curves for three conditions: (a) normal load, i.e. fully equipped with bunkers about half full, and reserve feed tanks empty; (b) deep load with all bunkers and tanks full; (c) light with all coal, water (except in boilers), ammunition, provisions and consumable stores removed . The curves for a cargo or passenger ship are generally drawn for the condition when light, when fully,laden with passengers or with a -25 the influence of beam and freeboard . homogeneous cargo, and sometimes for an intermediate condition; typical curves are given in fig . It . Stability curves are obtained on the assumptions ' . That all openings in the upper deck, forecastle and poop (if any) are covered in and made watertight; and the buoyancy of any erections above these decks is generally neglected . 2 .

That the

side of the ship is intact up to the upper deck, all side scuttles, ports or other openings being closed . 3 . That all weights in the ship are absolutely fixed . 4 . That no changes of trim occur during the inclination . In some cases curves are drawn (a) with forecastle and poop intact, (b) with these thrown open to the sea, the latter condition being more commonly considered . The slope of the stability curve for small angles, the maximum righting lever with the angle at which it occurs, and the range or the inclination at which the stability vanishes are of particular interest, inasmuch as the curve depends principally on these features; and the effect on them, particulars of variation of freeboard; breadth and position of centre of gravity, is considered below . The stability curve AA (fig . 12) is drawn for a box-shaped vessel of draught to ft., freeboard to ft. and beam 30 ft.; with C.G. in the water-plane . The curves EE, FF, GG are drawn for the same vessel, but with freeboard altered to 121, 72 and 5 ft . Effect of respectively; it will be observed that freeboard has no freeboard. influence on the stability at small angles, but has a marked effect on the range and maximum righting lever .